Gastrulation involves a number of cell interactions that ultimately establish the primary body plan. These morphogenetic rearrangements utilize cell recognition and adhesion and a host of other cellular functions to organize the ectoderm, mesoderm and endoderm. This project asks how pattern unfolds during gastrulation in the sea urchin embryo where a number of experimental approaches are uniquely possible. Molecules associated with several morphogenetic phenomena have been identified and several epigenetic interactions have been identified. Some of these have been characterized, others are known only phenomenologically, and the research has continued to identify experimentally, new cellular properties that participate in this dramatic phase of development. The goals are: (1)To complete the sequencing and functional characterization of hyalin and echinonectin, two extraembryonic cell adhesive substrates. Cells change their adhesiveness toward these molecules in germ layer-specific patterns and at specific times during gastrulation. As part of this goal, an attempt to Identify the receptors for these substrates will be made since the receptors are Implicated, experimentally, as having multiple roles in development. (2) To identify, purify and characterize, components involved in four crucial events of gastrulation: (a)During ingression of the primary mesenchyme cells there are four simultaneous adhesion changes. Molecular details are known for two of these so the focus will be to learn molecular details about the other two. (b)Endodermal cell rearrangements during archenteron invagination utilize cell convergence and extension as the primary mechanism of elongation of the primitive gut. Experiments will attempt to characterize adhesion molecules that participate in that morphogenetic movement, starting with extant candidate molecules. (c)A specific target has been identified as the anatomical destination of the archenteron at the end of its invagination. Experiments will attempt to identify marker molecules that are associated with that interaction. (d)Two bilaterally located patches of ectoderm have been found to regulate the pattern of spiculogenesis. The ectoderm cells in these patches somehow direct the underlying primary mesenchyme cells to organize and synthesize the skeletogenic apparatus at two anatomically-specific locations. The dorso-ventral and the animal-vegetal axes are critical for the spatial organization of these two sites. Experiments will attempt to learn how this positioning is established and the nature of the interaction between the ectoderm and the primary mesenchyme cells. These interactions are both adhesive and involved in information transfer to establish embryonic pattern.